46 FLORA. 



18. Potamogeton crispns L. CURLED-LEAVED PONDWEED. (I. F. f. 159.) 

 Steins branching, compressed. F^eaves 2-ranked, linear-oblong or linear-oblanceo- 

 late, sosilr or semi-amplexi am, obtuse, serrulate, crisped, 1-10 cm. long, 6-14 

 mm. wide. 3 7 nerved, the midrib often compound and the outer nerves very near 

 the margin; stipules small, scarious, obtuse, early perishing; peduncles 2-5 cm. 

 long, frequently recurved in fruit, sometimes very numerous; spikes about 1 cm. 

 lone, appearing very bristly with the long-beaked drupelets when in fruit ; fruit 

 ovoid, about 3 mm. long, 2 mm. or more wide, 3-keeled on the back, the middle 

 keel with a small projecting tooth near the base, the face slightly curved, the style 

 facial and nearly as long as the drupelet; embryo small, its apex pointing directly 

 toward its base. The plant is mainly propagated by peculiar winter buds. In 

 fresh, brackish or even salt water. Mass., Perm., and Va. Also in Europe. Aug. 



19. Potamogeton zosteraefolius Schum. Eel-grass Pondweed. (I. F. 

 f. 160.) Stems much flattened, sometimes winged, widely branching. Leaves 

 linear, obtuse and mucronate or sharp-pointed at the apex, 5-30 cm. long, 2-5 mm. 

 wide, with 3 principal nerves and many fine ones; stipules scarious, obtuse, finely 

 nerved, soon perishing ; peduncles 3-10 cm. long; spikes cylindric, about I cm. 

 long, 12-15 -flowered ; fruit obovoid with a broad base, about 4 mm. long, 2.5-3 

 mm. thick, 3-keeled on the back, the lateral keels rather obscure ; face arched, 

 beaked with a short recurved style; embryo slightly incurved. The plant is prop- 

 agated by the terminal leaf-buds, which sink to the bottom, and rest during the 

 winter. In still or running water, N. B. to N. J., west to Or. Also in Europe. 

 July-Aug. 



20. Potamogeton Hlllii Morong. Hill's Pondweed. (I. F. f. 161.) Stems 

 slightly compressed, slender, widely branching, 0.3-0.6 m. long. Leaves linear, 

 acute, cuspidate, or often almost arista te, 2-6 cm. long, 0.5.-2.5 mm. wide, 3- 

 nerved, the lateral nerves delicate and nearer the margins than the midrib; stip- 

 ules whitish, many-nerved, obtuse, 6-10 mm. long; peduncles about 1 cm. long, 

 erect or slightly recurved; spikes capitate, 3-6-fruited; fruit obliquely obovoid, 

 obtuse at the base, about 4 mm. long, 2-2.5 mm - thick, 3-carinate on the back, 

 the middle keel sharp and more or less undulate, flat on the sides, face slightly 

 arched; style nearly facial, short; embryo coiled. In ponds, E. N. Y. to Mich. 

 There are two forms of the species, the one 2 -glandular at the base of the leaves, 

 the other glandless. July-Sept. 



21. Potamogeton foliosus Raf. Leafy Pondweed. (I. F. f. 162.) Stems 

 flattened, much branched, 0.3-1 m. long. Leaves 2-5 cm. long, 1-2 mm. wide, 

 acute, 3 -nerved; stipules white, hyaline, obtuse or sometimes acute, 1-2 cm. long; 

 peduncles more or less clavate, erect; spikes about 4-flowered; fruit lenticular or 

 nearly orbicular, about 2 mm. in diameter, 3-keeled on the back, the middle keel 

 winged, sinuate-dentate, often with projecting shoulders or teeth at each end, the 

 face strongly angled or arched, sharp, often with a projecting tooth at the base; 

 style apical. In ponds and streams, N. B. to Br. Col., Fla., N. Mex. and Cal. 

 July-Aug. (P. pauciflorus Pursh.) 



Potamogeton folibsus Niagardnsis (Tuckerm.) Morong. Larger. Stems 0.6-1. 



m. long, leaves sometimes over 7.5 cm. in length and 2 mm. wide, 3-5-nerved ; 



stipules larger and occasionally acute; spikes 8-12-flowered. Niagara Falls to Mich, 

 and Cal. 



22. Potamogeton obtusifolius Mert. & Koch. Blunt-leaved Pondweed. I 

 (I. F. f. 163.) Stems usually slender, compressed, widely branching. Leaves 

 linear, 5-8 cm. long, 1-4 mm. wide, obtuse, often mucronate, usually 3-nerved 

 with a broad midrib, sometimes 5 7 nerved, 2-glandular at the base, the glands 

 lar^e and translucent; stipules white or scarious. many nerved, obtuse. I -2 cm. 

 long, often as long a- or longer than the internodes; peduncles numerous, slender, 

 erect; spikes 6 8 mm. long, ovoid. 5 8-flowered; fruit obliquely obovoid, alxmt 3 

 mm. long and 1 mm. thick, .} keeled; style short, blunt, nearly facial. In still 

 water, Que. to 1'enn.. Minn., and Wyo. Also in Europe. July Aug. 



23. Potamogeton Friesii Ruprecht. Fries' Pondweed. (I. F. f. 164.) 

 Stems compressed, 0.5-1.3 m. long, branching. Leaves 36 cm. long, about 2 mm. 



